The present invention relates to a novel element for modulating area which exhibits function under action (application) of electric field.
In general, nano-technology is recognized as technology for observing, preparing (manufacturing) and utilizing fine structure having size of the order of one hundred millionth (10−8 m=10 nm).
In the latter half of the year of 1980, ultra-high precision microscopes called scanning type tunnel microscopes have been invented so that one atom and/or one molecule can be observed. If such scanning type tunnel microscopes are used, not only atoms or molecules can be observed, but also atoms or molecules can be operated (manipulated) one by one.
For example, the example where atoms are arranged on the surface of crystal to write characters, and the like have been reported. However, even if it can be said that atoms or molecules can be operated or manipulated, it is not practical to operate or manipulate, one by one, a huge number of atoms or molecules to assemble new materials (substances) or devices.
In order to operate or manipulate atoms or molecules, or cluster thereof to form a structure of the nanometer size, a new ultra precision processing technology to realize such a structure is required. As such a fine processing technology of the nanometer precision, two systems are know when roughly classified.
One system is a method conventionally used in manufacturing processes for various semiconductor devices. This method is, e.g., such a method of the so-called top-down type to precisely shave a large silicon wafer down to the minimum size to prepare integrated circuits. The other system is a method of the bottom-up type to assemble atoms or molecules as small parts or components serving as micro (very small) unit to manufacture a target nano-structure.
In connection with the limit as to what structure of small size can be manufactured by the top-down system, there is the famous Moore's Law that Gordon Moore who is co-creator of Intel Corporation has presented in 1965. This rule is the content that “the degree of integration of transistor becomes double in eighteen months”. Since 1965 (year), the semiconductor business world has enhanced degree of integration of transistor in accordance with the Moore's Law over thirty years.
International Technology Roadmap for Semiconductor (ITRS) for fifteen years in future announced from the U.S. Semiconductor Industrial Associates (SIA) indicates the opinion that the Moore's Law is continuously valid.
The ITRS consists of short-range roadmap until 2005 (year) and long-range roadmap until 2014 (year). In accordance with the short-range roadmap, process rule of the semiconductor chip is assumed to become equal to the order of 100 nm and the gate length of the microprocessor is assumed to become equal to 65 nm in 2005. In accordance with the long-range roadmap, the gate length is assumed to become equal to 20 through 22 nm in 2014.
As miniaturization of the semiconductor chip is advanced, operating speed becomes high and power consumption is suppressed accordingly at the same time. Further, the number of products (chips) taken from a single wafer and the production cost is also lowered. This is because makers for microprocessors compete the process rule and the degree of transistor integration of new products.
On November in 1999, the research group of USA indicated epoch-making research result of miniaturization technology. The research result is directed to a method of designing gate of FET (Field Effect Transistor) called FinFET, which has been developed by the group including Professor Chainmin Fuh, et al. who is in charge of Computer Science at Barkley School of California University. This method enables formation of transistors which are 400 times greater than that in the prior art on a semiconductor chip.
The gate is an electrode for controlling flow of electrons at the channel of FET, and is caused to be of structure, according to present typical design, in which the gate is placed in parallel to the surface of the semiconductor and serves to control the channel from one side. In this structure, it was considered that since if the gate has not a predetermined length or more, it is impossible to cut off (interrupt) flow of electrons, gate length therefore constitutes one cause (factor) to limit miniaturization of transistor.
On the contrary, in the case of the FinFET, the gate is caused to be of fork type bridging over both sides of the channel to effectively control the channel. In the structure of the FinFET, the gate length and the transistor can be further reduced as compared to the conventional structure.
The gate length of the FET of the prototype that the same research group as above has manufactured is 18 nm, which is one tenth of present typical gate length. This gate length is equivalent to the size in 2014 (year), which is indicated by the long-range roadmap of ITRS. Further, it is said that gate length which is one half thereof may be realized. Since Fuh, et al. do not have intention to acquire the Patent in anticipation that such structure will be widely employed in the semiconductor business world, there is also the possibility that the FinFET may also become main current of the manufacturing technology.
However, it is also pointed out that “Moore's Law” might reach the limit based on the natural law after all.
For example, in the semiconductor technology which is main current at present, circuit patterns are baked on silicon wafer by the lithography technology to manufacture semiconductor chip. In order to realize further miniaturization (fine structure), resolution must be increased. In order to increase resolution, a technology utilizing light having shorter wavelength must be put into practice.
Moreover, calorific value per semiconductor chip may become too large with increase of the degree of integration. As a result, the semiconductor chip caused to have high temperature may be erroneously operated, or thermally broken.
Further, in accordance with prediction by the specialist, it is considered that when the semiconductor business world continues to miniaturize (reduce) chip as it is, the facility cost and/or the process cost are increased so that manufacturing of semiconductor chip might become impossible from an economical point of view in about 2015 also since deterioration of yield is invited in addition to the above.
As a new technology for overcoming technical obstacle of the top-down system as described above, the spotlight of attention is focused on research for allowing individual molecules to have functions as electronic parts (components). Devices based on such research or study are electronic device consisting of single molecule (molecular switch, etc.), and are manufactured (fabricated) by the bottom-up system.
Also with respect to metal, ceramics and/or semiconductor, researches (studies) for preparing (manufacturing) structure of nano-meter size by the bottom-top system are being performed. However, if attention is drawn to molecules which are primarily and individually independent and have variety to the number of about several million kinds in difference of shape and/or difference of function, etc. to exhibit the properties thereof, it is possible to design, by the bottom-up system, devices (molecular devices) having features entirely different from conventional devices to manufacture such devices.
For example, width of conductive molecule is only 0.5 nm. Wire of this molecule enables realization of wiring having density which is several thousands times than that of line width of about 100 nm which is realized by the present integrated circuit technology. Moreover, when, e.g. one molecule is used as memory element (device), recording which is ten thousands times or more than that of DVD (Digital Versatile Disc) can be made.
Molecular devices are synthesized by chemical process differently from the conventional semiconductor silicon. In 1986, Yuji Hizuka of Mitsubishi Denki Kabushiki Kaisha has developed the first organic transistor consisting of polythiophene (polymer) in the world.
Further, search group of U.S. Hewlett-Packard (HP) Corporation and Los Angeles school of California University succeed manufacturing of organic electronic device and announced the content thereof in Science Magazine on July in 1999. Such organic devices are disclosed in U.S. Pat. No. 6,256,767 specification and U.S. Pat. No. 6,128,214 specification. They made (fabricated) switches by using molecular films consisting of several millions of rotaxane as organic molecule to connect these molecular switches to make AND gate serving as a basic logical circuit.
In addition, cooperative search group of the Rice University and the Yale University in U.S.A. succeeded to make molecular switch in which molecular structure is changed by electron injection under application of electric field to perform switching operation and announced such molecular switch on the Science Magazine on November in 1999 (J. Chen, M. A. Reed, A. M. Rawlett and J. M. Tour, “Large on-off ratios and negative differential resistance in a molecular electronic device”, Science, 1999, Vol. 286, 1551-1552, J. Chen, M. A. Reed, C. Zhou, C. J. Muller, T. P. Burgin and J. M. Tour, “Conductance of a molecular junction”, Science, 1997, Vol. 278, 252-2). The function to repeatedly perform on-off operation is a function which was not realized by the group of HP (Hewlett-Packard) Corporation and Los Angeles school of California University. The size thereof is one millionth of ordinary transistor, and constitutes basis for manufacturing small and high performance computer.
Professor J. Tour (Rice University, Chemistry) who succeeded synthesis stated that since high cost clean room used for ordinary semiconductor manufacturing process is unnecessary, production cost of molecular switch can be reduced down to one several ten thousandth of prior art. Within five to ten years, he has a schedule to make hybrid type computer of molecule and silicon.
In 1999, Bell Laboratory (Lucent Technology Corporation) fabricated organic thin film transistor by using pentacene single crystal. This organic thin film transistor exhibited the characteristic equivalent to inorganic semiconductor.
Although it is said that studies or researches of molecular device having a function as electronic component are extensively being performed, most of studies relating to molecular devices until now were directed to studies in which drive is performed by light, heat, proton or ion, etc. (Ben L. Feringa, “Molecular Switches”, WILEY-VCH, Weinheim, 2001).
As conventional molecular element driven by electric field, there only existed element utilizing change of material property of molecule itself which has been caused to undergo action (application) of electric field, i.e., element in which electronic state of molecule itself considered to be single element is changed by electric field. For example, in organic FET, carrier transfer (movement) in organic molecule is modulated by change of electric field exerted on organic molecule within the channel area.
In view of actual circumstances as described above, an object of the present invention is to provide a functional molecular element (device) effectively controlled by electric field on the basis of a new principle.